This invention relates to printing machines, and more particularly, to a toner development apparatus for developing latent electrostatic images on a charge-retentive surface and, more particularly, to an improved toner sump or storage area for dispensing single component magnetic developer for presentation to a magnetic developer roll which, in turn, presents the developer to a charge-retentive surface such as photoconductor.
In the art of xerography or other similar image reproducing arts, a latent electrostatic image is formed on a charge-retentive surface such as a photoconductor which generally comprises a photoconductive insulating material adhered to a conductive backing. The photoconductor is first provided with a uniform charge after which it is exposed to a light image of an original document to be reproduced. The latent electrostatic images, thus formed, are rendered visible by applying any one of numerous pigmented resins specifically designed for this purpose. In the case of a reusable photoconductive surface, the pigmented resin, more commonly referred to as developer or toner which forms the visible images is transferred to plain paper.
It should be understood that for the purposes of the present invention, which relates to the development of latent electrostatic images with developer or toner particles, the latent electrostatic image may be formed by means other than by the exposure of an electrostatically charged photosensitive member to a light image of an original document. For example, the latent electrostatic image may be generated from information electronically stored or generated in digital form which may afterwards be converted to alphanumeric images by image generation electronics and optics. However, such image generation electronic and optic devices form no part of the present invention.
Many acceptable techniques exist for applying developer; however, one general approach, which is often used commercially, it to attract particulate developer to an applicator surface and move the applicator into a transfer relation with the image member so that marking particles can adhere to the member in accordance with the image pattern. Most commonly, the applicator is a roller which rotates so that its peripheral surface moves between a developer supply location and a zone in transfer relation with the image member. Adherence of the developer to such applicator rollers can be accomplished in various ways including, e.g., adhesive or electrical attraction, but the most prevalent commercial technique utilizes magnetic attraction and applicators using this technique are often called magnetic brushes.
Developers used with such magnetic brushes can be single component (in which case toner is magnetically attractable) or comprise two components (in which case the toner particles are electrostatically attracted to magnetically attractable carrier particles in the developer mixture). The magnetic brush applicators can take various forms, however, a typical configuration comprises a non-magnetic outer cylinder which surrounds an array of magnets located within its inner periphery. Developer transport is effected by rotation of the outer cylinder and/or the interior magnet array.
In using such magnetic brushes (and in other applicators such as mentioned above), the uniformity of image-development often depends significantly upon control of the quantity and density (i.e., compactness) and uniformity of developer adhering to the applicator surface. Developer shortage can cause incomplete development and developer excess can cause scratching and other non-uniformities in the developed image. Developer shortage as well as excess can result from developer agglomeration.
Although single component developers offer many advantages over two component systems, many of these developers have a problem in that they tend to lump up or agglomerate in the developer sump to a greater degree than do two component developers. Also, it is difficult to meter the developer to the desired thickness on the developer roll.
The traditional technique for controlling brush thickness of such brushes has been a doctor blade that extends across the applicator surface and is spaced a uniform distance from the surface. Such doctor blade is located between the developer supply and the image member so as to trim off excess developer adhering to the roller. Thus, the blade is precisely positioned parallel to the transporting cylinder to form a predetermined gap which controls the amount or thickness of toner passing to the development zone. Proper blade positioning is critical and it is extremely difficult to achieve and maintain. An expensive mechanism is necessary if easy adjustment is needed. More often, compromises are made which make such blade difficult to adjust or not adjustable at all. In addition to the foregoing problems such blades necessarily cause unwanted compaction of the adhered developer, prior to its entering the development zone.
A method and apparatus for applying toner to a charge-retentive surface which purports to solve the problem of toner metering is disclosed and claimed in U.S. Pat. No. 4,227,796 issued in the name of Kamp et al and assigned to the Eastman Kodak Company. As disclosed therein, a coil spring is provided through which developer from a sump flows. The spring tension is adjustable to vary the flow rate therethrough and is mounted for rotation in order to break up an agglomerated developer as it passes through the spring.
The spring is mounted in intimate contact with the developer roll with which it is associated. It appears that the rotating coil spring acts like an auger of the type conventionally used in xerographic development and cleaning systems. Thus, the coils of the spring move through the developer while transporting it in the direction of the longitudinal axis of the developer roll to thereby uniformly distribute it on the surface of the the developer roll beyond the line of contact between the spring and the developer roll.
Structure similar to Applicant's invention is incorporated in the Model M10 copier machine by Ricoh Company, a Japanese Corporation. This machine was first introduced as a commercial product during the summer of 1984 which was subsequent to our invention and less than one year prior to the filing of a patent application on our invention. The developer apparatus of the Ricoh M10 machine utilizes a Mylar (Trademark of E. I. DuPont de Nemours & Co.) a blade for metering the developer onto a magnetic developer roll. The metering blade is fabricated from a ferromagnetic material and is mounted in intimate contact with the developer roll.
U.S. Pat. No. 4,188,907 discloses and claims a particle dispenser with a magnetically driven agitator immersed in developer particles. An oscillatory magnetic field created through the rotation of a roll magnet causes the agitator to vibrate to thereby preclude bridging and caking of the particles to improve the flow of the developer from the open end of a chamber.